1) MTC
With development of the internet of things, more and more attention has been paid to Machine Type Communication (MTC) to be supported in a Long Term Evolution (LTE) system.
A project has been launched in the 3GPP Release 13 for enhancement of the physical layer in MTC. An MTC device (or an MTC terminal) may be provided with a part of a plurality of Machine to Machine (M2M) communication characteristics, e.g., low mobility, a small amount of data to be transmitted, insensitivity to a communication delay, and a requirement of extremely low power consumption, where in order to lower the cost of the MTC UE, a new type of UE may be defined with only a 1.4 MHz radio frequency bandwidth supportable in the uplink and the downlink, respectively.
In an existing network, for a terminal operating in a scenario such as in a basement, in a shopping mall, or at a corner of a building, a wireless signal may be seriously blocked, and thus greatly attenuated, so that the terminal fails to communicate with the network, and if a coverage area of the network is extended in such a scenario, the cost of deploying the network will be greatly increased. As some tests have shown, the existing coverage area needs to be extended to some extent for communication over the network. A feasible practice to extend the coverage area is to transmit an existing channel repeatedly or to use some other similar technologies, and in theory, the coverage area can be extended to some extent by transmission of an existing physical channel repeated for tens or hundreds of times.
2) CSI-RS
In an LTE system, a Channel State Information-Reference Signal (CSI-RS) is transmitted via 1, 2, 4, or 8 antenna ports, i.e., antenna ports p=15, p=15, 16, p=15, . . . , 18, and p=15, . . . , 22 respectively. The CSI-RS is only defined in a configuration with a sub-carrier spacing Δf=15 kHz.
A plurality of CSI-RSes can be configured in a given cell, particularly as follows: a terminalis supposed to be configured with zero or one Non-Zero Power (NZP) CSI-RS; and the terminalis supposed to be configured with zero or a plurality of Zero Power (ZP) CSI-RSes; when some bits among 16 bits of a ZP CSI-RS configured via higher-layer signaling are 1, the terminal may posit zero power at CSI-RS positions of corresponding 4 ports unless these resource elements overlap with NZP CSI-RSes configured via higher-layer signaling, where the bits correspond to CSI-RS configuration numbers of the 4 ports in a one-to-one manner, and the first bit corresponds to the lowest CSI-RS index.
A CSI-RS only appears in a downlink slot, where a normal Cyclic Prefix (CP) satisfies the conditions depicted in Table 1, an extended CP satisfies the conditions depicted in Table 2, and the CSI-RS is transmitted in a downlink sub-frame determined according to a sub-frame configuration period TCSI-RS and a sub-frame offset ΔCSI-RS of the CSI-RS, as listed in Table 3, that is, the sub-frame including the CSI-RS satisfies (10nf+└ns/2┘−ΔCSI-RS) mod TCSI-RS=0, where “mod” represents a modular operation, nf represents a radio frame number, and ns represents a slot number. Both an NZP CSI-RS and a ZP CSI-RS can be configured respectively as a configuration index parameter ICSI-RS in Table 3.
The terminal posits no CSI-RS to be transmitted in the following cases: a special sub-frame in a frame structure type 2; a sub-frame in which a CSI-RS conflicts with a synchronization signal, a Physical Broadcast Channel (PBCH), and a System Information Block Type-1 (SIB-1); and a sub-frame in which paging information is configured.
TABLE 1Configured CSI-RS resourcesCSI-RS1 or 248configuration(k′, l′)ns mod 2(k′, l′)ns mod 2(k′, l′)ns mod 2Frame structure0(9, 5)0(9, 5)0(9, 5)0types 1 and 21(11, 2) 1(11, 2) 1(11, 2) 12(9, 2)1(9, 2)1(9, 2)13(7, 2)1(7, 2)1(7, 2)14(9, 5)1(9, 5)1(9, 5)15(8, 5)0(8, 5)06(10, 2) 1(10, 2) 17(8, 2)1(8, 2)18(6, 2)1(6, 2)19(8, 5)1(8, 5)110(3, 5)011(2, 5)012(5, 2)113(4, 2)114(3, 2)115(2, 2)116(1, 2)117(0, 2)118(3, 5)119(2, 5)1Only frame20(11, 1) 1(11, 1) 1(11, 1) 1structure type 221(9, 1)1(9, 1)1(9, 1)122(7, 1)1(7, 1)1(7, 1)123(10, 1) 1(10, 1) 124(8, 1)1(8, 1)125(6, 1)1(6, 1)126(5, 1)127(4, 1)128(3, 1)129(2, 1)130(1, 1)131(0, 1)1
TABLE 2Configured CSI-RS resourcesCSI-RS1 or 248configuration(k′, l′)ns mod 2(k′, l′)ns mod 2(k′, l′)ns mod 2Frame structure0(11, 4) 0(11, 4) 0(11, 4) 0types 1 and 21(9, 4)0(9, 4)0(9, 4)02(10, 4) 1(10, 4) 1(10, 4) 13(9, 4)1(9, 4)1(9, 4)14(5, 4)0(5, 4)05(3, 4)0(3, 4)06(4, 4)1(4, 4)17(3, 4)1(3, 4)18(8, 4)09(6, 4)010(2, 4)011(0, 4)012(7, 4)113(6, 4)114(1, 4)115(0, 4)1Only frame16(11, 1) 1(11, 1) 1(11, 1) 1structure17(10, 1) 1(10, 1) 1(10, 1) 118(9, 1)1(9, 1)1(9, 1)119(5, 1)1(5, 1)120(4, 1)1(4, 1)121(3, 1)1(3, 1)122(8, 1)123(7, 1)124(6, 1)125(2, 1)126(1, 1)127(0, 1)1
TABLE 3CSI-RS sub-frameCSI-RSCSI-RS sub-frameconfigurationsub-frameConfiguration ICSI-RSperiod TCSI-RSoffset ΔCSI-RS0-45ICSI-RS 5-1410ICSI-RS-515-3420ICSI-RS-1535-7440ICSI-RS-35 75-15480ICSI-RS-75
3) MBSFN Sub-Frame
A Multicast-Broadcast Single-Frequency Network (MBSFN) is defined in the LTE system. In a radio frame, all the sub-frames other than a sub-frame 0 and a sub-frame 5 can be configured as MBSFN sub-frames in principle. An MBSFN sub-frame includes two areas, i.e., an MBSFN area and a non-MBSFN area. In the MBSFN area, there is no Cell-specific Reference Signal (CRS), which is also called Common Reference Signal, and there are CRSes in the non-MBSFN area. A Physical Multicast Channel (PMCH) is only transmitted using an extended CP in the MBSFN area of the MBSFN sub-frame, where the length (size) of the non-MBSFN area of the MBSFN sub-frame is preconfigured via high-layer signaling. A Physical Downlink Control Channel (PDCCH) can be transmitted in the non-MBSFN area of the MBSFN sub-frame, i.e., a control area, using a same type of CP as the sub-frame 0 to schedule a Physical Uplink Shared Channel (PUSCH) or a Physical Downlink Shared Channel (PDSCH). The length of the non-MBSFN area in the MBSFN sub-frame can be configured as 0, 1, or 2, where it can be configured as 0 for an MBSFN sub-frame in which only a PMCH is transmitted, and it can be configured as 1 or 2 for an MBSFN sub-frame in which transmission of a PDSCH is supported, dependent upon the number of CRS ports in the system, where if a CRS is configured for four antenna ports, it may be configured as 2, that is, two OFDM symbols are reserved for transmission of a PDCCH. A size of a control area in a non-MBSFN sub-frame can be 1, 2, or 3 as depicted in Table 4. A size of a Downlink Control Information (DCI) area indicated by a Control Format Indicator (CFI) transmitted in the non-MBSFN area of the MBSFN sub-frame is a same as the size of the non-MBSFN area preconfigured via high-layer signaling.
TABLE 4The number of OFDMThe number ofsymbols for a PDCCHOFDM symbols for aSub-framewith NRBDL >10PDCCH with NRBDL ≤10Sub-frames 1 and 6 in a frame structure1, 22type 2An MBSFN sub-frame supporting a1, 22PDSCH and configured with one or twocell-specific antenna portsAn MBSFN sub-frame supporting a22PDSCH and configured with fourcell-specific antenna portsA sub-frame supporting no PDSCH00A non-MBSFN sub-frame (except1, 2, 32, 3sub-frame 6 in a frame structure type 2)configured with a positioning referencesignalOthers1, 2, 32, 3, 4
Where NRBDL in the table is the number of RBs in a downlink system bandwidth.
A PDSCH can be transmitted in an MBSFN sub-frame other than the following MBSFN sub-frames: 1) an MBSFN sub-frame in which a PMCH needs to be received as instructed via higher-layer signaling; and 2) an MBSFN sub-frame configured to transmit a Positioning Reference Signal (PRS), where the PRS is only configured to be transmitted in an MBSFN sub-frame, and the sub-frame 0 is used with a normal CP. Currently, a PDSCH is transmitted in an MBSFN sub-frame only in the DMRS-based transmission modes 9 and 10 as shown in Table 5.
TABLE 5Mode 9DCIUse a Cell-RadioA non-MBSFN sub-frame: if theformat 1ANetwork Temporarynumber of PBCH antenna ports isIdentifierone, Single-antenna port, port 0 is(C-RNTI) andused (see TS36.213 Section 7.1.1),performotherwise Transmit diversity (seetransmissionTS36.213 Section 7.1.2).in common andAn MBSFN sub-frame:UE-specific searchSingle-antenna port, port 7space(see TS36.213 Section 7.1.1)DCIUse a C-RNTI andup to 8 layer transmission, ports 7-14format 2Cperformsee TS36.213 Section 7.1.5B) ortransmission insingle-antenna port, port 7 or 8 (seeUE-specific searchTS36.213 Section 7.1.1)spaceMode 10DCIUse a C-RNTI andA non-MBSFN sub-frame: If theformat 1Aperformnumber of PBCH antenna ports istransmission inone, Simile-antenna port, port 0 iscommon andused (see TS36.213 Section 7.1.1),UE-specific searchotherwise Transmit diversity (seespaceTS36.21.3 Section 7.1.2)A MBSEN sub-frame:Single-antenna port, port 7 (seeTS36.213 Section 7.1.1)DCIUse a C-RNTI andup to 8 layer transmission, ports 7-14format 2Dperform(see TS36.213 Section 7.1.5B) ortransmission insingle-antenna port, port 7 or 8 (seeUE-specific searchTS36.213 Section 7.1.1)space
In order to reduce repeated times as many as possible, some studies have shown that channel estimation across sub-frames (joint channel estimation) is a working approach. The so-called channel estimation across sub-frames refers to joint channel estimation using reference signals in a plurality of sub-frames, and a typical practice is to average results of channel estimation of the plurality of sub-frames with a corresponding weight. Correspondingly, data parts in the plurality of sub-frames also need to be combined (at a symbol level or a bit level). They are combined on the precondition of a same length of transmission signals in the plurality of sub-frames to be combined.
However in the prior art, CSI-RSes are transmitted over specific Resource Elements (REs) in a configured period, and there are different CSI-RS conditions in different downlink sub-frames, so that there are different numbers of available REs when mapping resources for data transmission; and an MBSFN sub-frame and a non-MBSFN sub-frame differ from each other in terms of a reference signal, a size of a control area, and etc., so that there are different numbers of available REs when mapping resources for data transmission. Thus there are different target numbers of coded bits resulted from the channel encoding and rate matching of the data, that is, the data transmitted repeatedly in the plurality of sub-frames cannot be combined across the sub-frames.
In summary, it is desirable to provide a method for repeated transmission of downlink data so as to enable the data to be combined across a plurality of sub-frames for channel estimation.